Non-scientifically, and assuming people above didn't double post and I can count....
#1 powder listed : IMR 4064 (9 mentions)
#2 would be IMR 3031 with 6 mentions
then, each with 5 mentions are BCL(2), IMR 4895, IMR 4320, and Alliant Reloader 15.
Thanks to all for your comments! Not sure why, but I note that Accurate Arms/Western Powders are not mentioned much at all. IMR totally dominates with 4 of the top 6 "favourite" powders (again, other than my personal choice, Varget)
(standard disclaimers apply...)